Gigantic Effect Due to Phase Transition on Thermoelectric Properties of Ionic Sol-Gel Materials

Sol-gel phase transition in ionic thermoelectrical (i-TE) materials can induce large rapid changes in viscosity and ionic transport process. Based on these properties, the phase-transition is expected to give a drastic variation in thermoelectric properties, crucial in low-grade waste heat harvesting for Internet of thing (IoT) and wearable electronic applications. In this work, we prepare and examine four different types of i-TE materials featured with non-phase-transition, thermal sol-to-gel phase transition, thermal gel-to-sol phase-transition and UV-induced sol-to-gel phase transition. For the first time, we observe a significant rise of the thermopower by around 6.5 times during the sol-gel transition of the poloxamer/LiCl system (thermal sol-to-gel phase-transition system). In addition, due to the stable value of electrical conductivity and thermal conductivity during phase transition, an even greater ionic figure of merit by around 23 times is also achieved. These phenomena are found to be universal as the large variation in thermopower is confirmed in the other thermal gel-to-sol transitional and UV-induced transitional materials. We further reveal the mechanism based on the Onsager's relations and propose a model that can deal with the pre-, post- and during phase-transition processes. Finally, we probe six factors that can influence the huge variation of the thermopower during the phase transition and shed light on the possible gigantic changes in thermopower during the phase transition. This work indicates the gigantic effect that phase transition can have on thermoelectric properties in i-TE systems regardless of the type of phase transition and discovers a possible route to design and control the desired TE performances of materials, which can lead to a new sight in tunable i-TE devices for low-heat energy harvesting applications.<br/><br/>References:<br/>Liu, J., Zeng, W., Tao, X., Gigantic Effect due to Phase Transition on Thermoelectric Properties of Ionic Sol–Gel Materials. <i>Adv. Funct. Mater.</i> 2022, 2208286. https://doi.org/10.1002/adfm.202208286